The present invention relates to CMOS driver circuits which provide data for transmission to a remote location. Specifically, a differential signal driver comprising CMOS circuit elements which can provide an analog differential voltage for transmitting 800 megabits of data per second is described.
Data transfers between computing devices are occurring at increasing speeds. This is particularly true for I/O communications between work stations and a server, as well as between personal computers and peripheral devices. The data transmissions from an I/O port of one device to an I/O port of another device are through a coaxial cable which has a characteristic impedance of 50 ohms. These transmission lines are usually driven differentially, i.e., first and second complementary analog signals, representing a data bit, are applied to a conductor of each transmission line. In order to generate analog data signals in the 600 MHZ/1.2 gigabits per second range, circuit components which can operate at these frequencies are needed. In the past, emitter coupled logic was the usual choice since it is capable of the high frequency switching necessary to transmit these higher data rates. The emitter coupled logic, however, dissipates considerably more power than conventional CMOS logic, and is also relatively more expensive to implement than CMOS circuit elements.
The driver circuit for sending data over these transmission lines ideally produces a differential voltage swing which is between 250 and 400 Mv under all operating conditions as set forth in the appropriate IEEE standard. Maintaining this voltage swing over various environmental conditions, including changes of temperature and changes in power supply voltage levels, provides for efficient power consumption while producing reliable switching signals which can be sensed by a receiver terminating the transmission lines.